Forsooth
/fərˈsuːθ/
Definition 1 of 1
Pro Tip 1/3Historical Flavor
Used to provide an old-fashioned or Shakespearean feel to language. 
Good sir, forsooth, I bid thee welcome.
Pro Tip 2/3Emphatic Agreement
Expresses strong agreement or confirmation, similar to saying 'indeed' with emphasis. 
Forsooth, the tale you speak of is as old as time itself.
Pro Tip 3/3Irony or Sarcasm
Sometimes used ironically or sarcastically to mock someone's statement. 
Ah, forsooth, as if I would ever trust a knave like you!